1. Field of the Invention
This invention relates to an improved lubricant seal structure and to an improvement over the method for making seals shown in U.S. Pat. No. 3,004,298; it also relates to an improvement over the product of U.S. Pat. No. 3,010,748.
2. Description of the Prior Developments
U.S. Pat. No. 3,004,298 set forth what was then a radically new method for making fluid seals, a method which resulted in better products than had been available earlier, and which provided more reliable and less expensive molding processes. The present invention preserves all of the benefits of this earlier invention, while giving greatly improved results in certain parts of the method which had over the years created problems.
The metal case in U.S. Pat. No. 3,004,298 is provided with a radial flange which, during manufacture, is placed in a mold that exerts two opposing pressures on the flange. This results in bending or reforming the terminal portion of the radial flange during the molding process to form a seal with a bent inner end surrounded with elastomer. As molded, the inner end of the seal is free from flash.
This prior forming method, especially as applied to a seal where the radial flange extends inwardly from the periphery of the case, exerted a strong inward pulling force upon the metal flange. This force also acted on the cylindrical periphery of the case. The force, sometimes called "heel pull" because it radially pulls in the heel of the metal case, has often been too large to be tolerated, resulting often in a reduction of the outside diameter of the case of up to about 0.01 inch.
The initial metal case stamping operation, which precedes the molding, tends to produce a case with a slightly concave axially extending peripheral portion, the concavity being generally in the order of from 0.001" to 0.015". The outer periphery is permitted tolerances at the heel within a range of from +0.003" to -0.002" so the stated concavity may not seriously affect the press fit of the seal case of the finished seal when it is installed in a machine part. However, a heel pull of 0.010" makes it impossible for the outer periphery to hold the permitted tolerance on the heel, which is where the primary press fit of the finished seal is achieved when it is installed in its intended machine part. Even a heel pull of 0.004" to 0.005" is unsatisfactory and cannot be accepted. A pull that is two or three times as great as that is clearly unacceptable. This heel pull also tends to produce an action called "bulbing" of the radial flange which can create unsatisfactory conditions affecting the quality of the finished part.
The present invention solves the problem of excessive heel pull and provides better tolerances and more uniform parts by reducing the amount of variation in the seal's outer periphery that resulted heretofore from the molding operation.
Thus, one object of the invention is to minimize heel pull and to minimize the reduction in the outer diameter of the metal case which is due to its radial flange being drawn in by the reform or bending phase of the molding process.
Another object of the invention is to reduce the amount of tonnage necessary to achieve the reform--i.e., the bending of the flange--in the mold cavity. One reason for wanting to reduce this tonnage is to make it possible to provide more cavities in the same mold press without having to increase the overall tonnage. Where the required tonnage per part is too large, fewer cavities are possible; where the tonnage per part can be reduced, then more cavities can be used in the mold press with the same overall tonnage. Alternatively, the total tonnage per press can be reduced, if desired.
Another object is to achieve a more consistent and distinct reform or bending operation, improving the mold closure, and also improving the trim qualities of the finished part.
The product and the method of this invention thus relate to a known system of flashless molding and simultaneous bonding of an elastomeric sealing lip to a rigid annular metal case element. In the known method, as best set forth in U.S. Pat. No. 3,004,298, pressure is applied in a first direction against a first face of the case element along a first circular line with a first forming edge of the die adjacent to but spaced from the inner periphery of the case element. Simultaneously, pressure is applied in a second, opposite direction against a second, opposite face of the case element along a second circular line with a second forming edge of the die which is concentric with the first circular line and first forming edge of the die. The second circular edge is radially outwardly spaced from the inner periphery of the case element and radially outwardly spaced from the first circular line or edge of the die. These two opposed pressures bend an annular peripheral margin along the case element at an angle to its radially extending portion.
Meanwhile, elastomeric material is forced against the exposed surfaces of the case element between the first and second lines and corresponding edges of the die and around the inner periphery of the case element, thereby bonding the elastomeric material to the case element, without flash, by the applied axial pressure.